Hi! Details on the matriculation rate of the program are not released to the students/not public knowledge. My personal take on the reason people drop is that the program is simply rigorous. Individuals have to adapt their study methods and put in the time to learning the material in a way that allows them to perform, but there are students who don't do this.
The unfortunate (but necessary) reality of this program is there is little wiggle room when it comes to poor exam performance. It is crucial that students try and seek help before they tank an exam, or reach out to staff for additional steps. People drop for all types of reasons, of which is majorly academic from what I have seen. It's not to say that DPMS does not care about their students, they do, but this program demands all of your time and resources (including emotional, physical, etc).
Per administrative staff, drop out rates from these past two years are no different from what they've been throughout the length of this program. I promise you (and all future applicants), if you put in the work, you will see your reward!